"The site is itself a response to whoever did this repulsive act because it symbolises both the exactions and horrors of the Nazi regime and the French people's power of resistance," the mayor added.

The stone lies next to the Avenue of the Righteous, which is dedicated to non-Jews who risked their lives to save Jews during the Holocaust, Ries noted.

"A new incident of anti-Semitism in our town," Deputy Mayor Alain Fontanel added on Twitter, posting a picture of a large black marble slab that had been knocked off its plinth.

"Quai Kleber synagogue was burnt down by the Nazis nearly 80 years ago. The memorial stone which marked this tragedy was vandalised overnight."

Fontanel said the mayor's office was working with police to track down those responsible for the act.

The synagogue, which was the Jewish community's main place of worship in the city, was ransacked and burnt to the ground by Hitler Youth on September 30, 1940.

The region was already shaken on February 19 when 96 graves were daubed with swastikas at a Jewish cemetery in Quatzenheim, northwest of Strasbourg.

Thierry Roos, a spokesman for the Israelite Consistory of the Lower Rhine region, said his community was "appalled by the degradation of the memorial, whether it was intentional or not,"

"They wanted to erase the memory of the synagogue on Quai Kleber by destroying it twice," Roos said.

A statement issued by the regional prefecture said that "anti-Semitism strikes at values of the Republic shared by all French citizens. No display of intolerance must threaten our ability to live together."

France is home to Europe's largest Jewish community and the third largest on the planet, with over 500,000, but has seen a surge in anti-Semitic violence and hate speech. Last month the Interior Ministry reported a 74% rise in antisemitic acts in 2018, prompting soul-searching throughout the country.